Introduction to the Nervous System Chapter 35 Of all the Nerve! Introduction to the Nervous System Chapter 35

Organs of the Nervous System Brain Spinal cord Numerous nerves Specialized sense organs such as eyes and ears Microscopic sense organs such as those found in the skin

Divisions of Nervous System Central Nervous System Processing system Brain and Spinal Cord Peripheral Nervous System Connects CNS to limbs and organs Somatic - Voluntary and Autonomic - Involuntary Autonomic = automatic CNS - Brain, spinal cord PNS - Nerves that extend to the periphery of body Autonomic nervous system - involuntary functions (breathing rates, respiratory rates, etc) Somatic - voluntary functions (motor neurons)

Neurons What do they do? 3 parts: carry the impulses that make things happen. cell body, branching projections called dendrites and elongated axons. Axons send signals, dendrites receive signals.

Axon is covered in ________________. Myelin is formed by ____________ __________. Nodes of Ranvier - Myelin Schwann cells are indentations between adjacent Schwann cells that aid in quick transmission of signals Compare nerve impulse speed of giant squid to human impulse speed

Conduction jumps from node to node, much faster than without myelin to insulate.

Nerve Bundle Organization White matter - has myelin Each axon in a nerve is surrounded by fibrous connective tissue called endoneurium. Groups of these axons are called fascicles which are surrounded by perineurium Epineurium covers whole nerve (fibrous sheath)

Reflex Arcs - no brain involvement

Nerve Impulses are Electrical Self propagating wave of electrical disturbance that travels along the surface of a neuron’s plasma membrane. Stimulus occurs Charges across the membrane change from - to + This change “travels” down the membrane of axon Synapse occurs at terminal end of presynaptic neuron Post synaptic neuron receives impulse and carries on the “message” or signal

The connection between the axon of one neuron and the dendrite of another is a SYNAPSE Space between neurons is called a synaptic cleft. Because of this gap, the electrical impulse (action potential) cannot be transmitted directly and must be converted into a chemical signal that is then converted back into an electrical signal in the postsynaptic cell. Neurotransmitters are held in vesicles until the impulse causes them to be secreted into the cleft and then recpetors on the postsynaptic cell receive the. The chemicals that convert the signal across the cleft are called neurotrasnmitters.

Action Potential Video http://www.youtube.com/watch?v=4j3_b5NVBiE

Neurotransmitters - There are at least 60 different neurotransmitters Neurotransmitters - There are at least 60 different neurotransmitters. - One type can trigger many different responses, depending on the postsynaptic cells receptors - list of major ones and their actions: http://thebrain.mcgill.ca/flash/i/i_01/i_01_m/i_01_m_ana/i_01_m_ana.html - 2